1. Field of the Invention
The present invention relates to a process for preparing an aromatic vinyl compound, in particular crystal-clear polystyrene, by anionic polymerization, the monomer or monomers and the organometallic compound serving as starter (initiator) being added in solution to a tubular reactor operating essentially without backmixing.
2. Description of the Relevant Prior Art
The following documents are cited:
______________________________________ EP 176 611 U.S. Pat. No. 3,030,346 EP 471 550 U.S. Pat. No. 3,954,894 U.S. Pat. No. 482,391 U.S. Pat. No. 4,196,153 U.S. Pat. No. 3,035,033 U.S. Pat. No. 4,200,713 U.S. Pat. No. 4,883,846 U.S. Pat. No. 4,205,016 ______________________________________
Loop reactors, i.e. tubular reactors that loop back into themselves, are described in EP-A 176 611 and U.S. Pat. No. 3,035,033 for the preparation of anionic polystyrene. It is recommended that the residence time be at least 1 to 3 hours and that the circulating volume be at least 15 times and preferably at least 25 times as large as the feed volume. Accordingly, only a small space-time yield is achieved by such a process, i.e. a very large, complex apparatus is required for production on an industrial scale.
U.S. Pat. No. 4,883,846 describes a process for the anionic polymerization of styrene, in which styrene in ethylbenzene is adiabatically polymerized in a reactor using n-butyllithium.
The disadvantage of this process is that only relatively small styrene concentrations can be used, so as not to let the final temperature rise too high since too high a final temperature would lead to a thermal termination and thus to an incomplete reaction and uncontrolled molecular weight distribution. Consequently, also only a small space-time yield is achieved.